Noise reduction tunnel, A10 motorway
Autobahnen- und Schnellstraßen-Finanzierungs-
GEOCONSULT ZT GmbH, Salzburg
General contractor: Felbermayr Bau GmbH,
Waterproofing: ISO-M GmbH
August 2013 to July 2017
The A10 motorway in Austria is one of the key northsouth links through the Alps. To reduce noise disturbance to the village population in Zederhaus, the decision was taken to enclose a 1.5 km long section of the motorway. The waterproofing system specified for installation by the general contractor had the disadvantage that any leakages would have allowed the uncontrolled spread of water below the membrane, with large-scale structural damage as a possible consequence.
For the waterproofing subcontract tender, HUESKER provided the project team with a conclusive, reliable and economical solution to this problem by developing the “infiltration-proof double membrane”. The adopted solution involves the placement of fill material in the trapezoidal gap between the cut-and-cover tunnel tubes prior to the start of waterproofing so as to create a single, integral profile embracing both tubes. The resulting crossfalls ensure that the water drains away easily from the critical area. The first component of the double membrane system, the geosynthetic clay liner (GBR-C), is installed directly on to the concrete surface as the secondary waterproof barrier. The factory-applied bentonite edge layer ensures that even vertical overlaps remain watertight. The direct contact pressure with the concrete automatically prevents the infiltration and spread of water behind the liner. The clay liner also provides a suitable base for the immediately overlying primary waterproofing layer, comprising a 2 mm PE-HD polymer membrane. The hot-wedge weld seams, arranged perpendicular to the longitudinal tunnel axis are testable with compressed air. In the unlikely event of any leakages in this membrane, the underlying Clay liner provides an “infiltration-proof” second line of defence to prevent the uncontrolled spread of water over the concrete surface. To protect the waterproof barrier while facilitating the run-off of precipitation, a Drainage and protection mat is installed directly over the double membrane as the top system layer. Finally, the entire enclosure is covered over with some 260,000 m³ of soil and vegetation. For the 1,200 residents of the municipality of Zederhaus, the motorway enclosure scheme will result in a significant improvement in their quality of life.
With its testable hot-wedge double seams arranged perpendicular to the tunnel axis, the primary PE-HD waterproof barrier offers long term reliability, with additional protection offered by the self-healing, secondary geosynthetic clay liner. Thanks to its straightforward and efficient installation, the innovative, sustainable waterproofing system also delivers a highly cost-effective solution.